1. Field of the Invention
The present invention relates to an optical disk apparatus and, in particular, to techniques for decreasing the data access time in an optical disk apparatus during a read or write operation thereof.
2. Description of the Related Art
An optical disk apparatus includes an optical pickup having an optical system for writing and reading data to and from a recording medium. A general construction of an optical pickup 1 is shown in FIGS. 5-7. The optical pickup 1 includes an optical unit 3 for searching for a laser beam to read or write the data to be recorded along a track of a recording medium 2, and an optical system (not shown) for receiving a reflected light from the recording medium 2. The optical unit 3 is supported by a base 4 so as to be capable of moving in an up-and-down direction corresponding to an optical axis A, as indicated in FIG. 7 by arrow X, and moving in a right-and-left direction perpendicular to the optical axis A, as indicated in FIG. 7 by arrow Y. That is, the optical unit 3 is supported by the base 4 such that it can rock in a direction indicated by Y', and includes a supporting axis 3P as its starting point. The up-and-down movement (arrow X) of the optical unit 3 functions as a focus control for the recording medium 2, whereas the right-and-left movement of the optical unit (arrow Y) functions as a track jump to position the optical axis A on an access target track in the recording medium 2. In general, the above movements can be performed by electronics 5 disposed in the base 4. Further, as shown in FIG. 5, the optical pickup 1 is supported by an arm 6 which slides on a guide bar 7, thereby allowing the optical pickup 1 to move along the recording medium 2 by a driving system (not shown) in the direction indicated by arrow Z. This functions as a feed seek to roughly position the optical pickup 1 on a track near an access target track.
An access operation of the optical pickup 1 in the recording medium 2 can be performed by a feed seek operation followed by a track jump operation. Specifically, during such an operation, the optical pickup is roughly positioned on a track near the access target track through the feed seeking operation. Then, the optical axis is finally positioned on the access target track through the track jumping operation. By way of example, if a maximum operating range capability for track jumping in the right-and-left direction (arrow Y, FIG. 7) is set to 200 tracks, the optical pickup 1 is positioned on a track within 200 tracks from the access target track through the feed seeking operation. After that, position data, which is generally referred to as MSF (where M stands for minute, S stands for second and F stands for frame), of the track where the optical pickup is positioned through the feed seeking operation is read. The track jump operation is then performed for the number of tracks corresponding to the difference between the positioned track and the access target track. A driving control of the feed seek operation is performed by applying a voltage to a driving motor so as to position the optical pickup on a track within 200 tracks from the access target track. Therefore, because control conditions of the feed seek are determined by the maximum operating range for the track jump operation, if such range is narrow, the optical pickup can be positioned with high accuracy through the feed seeking operation. However, in order to position the optical pickup with such high accuracy through the feed seeking operation, it is necessary to employ a braking mechanism to control the movement speed of the optical pickup during the feed seek operation, or to stop the movement thereof, which provides for a longer time for performing the feed seek operation.
The maximum operating range of the track jump operation having an effect on the feed seek speed will now be explained in further detail. Referring to FIG. 6, the right-and-left movement (arrow Y, FIG. 7) of the optical system during the track jump operation is generally performed by electronic equipment 5. Such movement is regularly limited to operate in the mechanical structure of the electronic equipment, because a member 3P of the optical unit 3 reaches to an element 5P comprised of the electronic equipment 5. In this situation, it is impossible to perform the focus control of the optical pickup. Therefore, the maximum operating range for the track jump operation should be set below an operating limitation range, and the track jump operation should be performed within the maximum operating range.
The maximum operating range for the track jump operation has an important effect on the features of the electronic equipment in the optical disk apparatus or the supporting unit of the optical unit included therein. For this reason, an attempt to perform a track jump operation is conducted on every predetermined manufacturing lot. Based on the results of such attempt, the maximum operating range for the track jump is set, for example, in accordance with the maximum number of tracks to track jump, a maximum applied voltage to the electronic equipment, or the longest applied time of the voltage. However, the feature of the electronic equipment or the feature of the supporting unit of the optical unit depends upon the environmental conditions in which the optical disk apparatus is used. Therefore, if a previously set condition for the maximum operating range is not optimal, there is a phenomenon generated due to such improper condition which causes the maximum operating range to appear narrower than the operating limitation. In this case, the control condition for the feed seek operation is set in accordance with the maximum operating range which is narrower than the operating limitation. As a result, the feed seek operation is performed with high accuracy, but at the same time becoming unnecessarily longer for feed seeking.
Furthermore, the track jump operation can come into question itself. That is, the track jump is performed from the currently positioned track toward the access target track. Here, the right-and-left movement of the optical system (arrow Y, FIG. 7) for the track jump operation is controlled by a voltage control according to the number of tracks between the currently positioned track and the access target track. For example, if the number of tracks to be track jumped is about 100 tracks, the length of time in which to apply the voltage is set in correspondence with the above 100 tracks. As mentioned above, the true right-and-left movement (arrow Y, FIG. 7) of the optical system is affected by either the feature of the internal voltage applied to the optical disk apparatus or the feature of the supporting unit of the optical system included therein. For this reason, similar to the maximum operating range, an attempt to perform the track jump operation is performed on every predetermined manufacturing lot. Based on the results of such attempts, the optimal time for the applied voltage is previously set in accordance with the number of tracks to be track jumped. Since either the feature of the electronic equipment or the feature of the supporting unit of the optical unit is affected by the environmental conditions in which the optical disk apparatus is used, the accuracy of the track jump operation deteriorates as a result of the previously set time for applying voltage not being an actual optimal time. As a result, it is impossible to position the optical pickup on the access target track by performing the track jump operation just one time. Moreover, if the optical pickup is unable to be positioned on the access target track on one track jump operation, the track jump is repeatedly performed from the track which was first jumped to, and if the access target track is still not accessed, the track jump operation is repeatedly performed again. Consequently, this causes an unnecessary increase in the number of times that the track jump operation must be repeated.
As mentioned above, both the accuracy (speed) of the feed seek operation by the optical pickup and the number of times in which the track jump operation of the optical system must be performed has a direct effect on the access time for writing or reading data in the optical disk apparatus. Therefore, in order to decrease the access time, the accuracy of the feed seek operation should be optimized, and the optical pickup should be finally positioned on the access target track with a minimal number of track jump operations.